In a gas turbine installed in a cold district, air taken in from the atmosphere is heated, and then let into the gas turbine.
This is because if high-density outside air (air) at an extremely low temperature (e.g., −20° C. to −30° C.) is taken, unchanged, into the gas turbine, ignition performance lowers or combustion vibration occurs, making it impossible to ensure the stable combustion of the gas turbine. If such air at the extremely low temperature is taken in, moreover, water in air may freeze into ice at the inlet of the gas turbine. The resulting ice may enter the gas turbine, damaging the turbine blade or the like.
In the gas turbine installed in the cold district, therefore, air is heated by a heating device, such as a heat exchanger, and then taken into the gas turbine. In this case, air is heated so that the air temperature reaches a temperature at which the gas turbine can perform stable combustion (e.g., a temperature of the order of +5° C.).
FIG. 3 shows an example of a gas turbine plant installed in a cold district. As shown in this drawing, a gas turbine 10 is composed of a compressor 11, a combustor 12, and a turbine 13 as main members. Air (atmosphere) A let in from the outside is taken into the compressor 11 of the gas turbine 10 via an air intake duct 15.
An inlet guide vane (IGV) 11a is provided at the inlet of the compressor 11, and the amount of air taken into the compressor 11 is controlled according to the opening degree of the IGV 11a. The opening degree of the IGV 11a is controlled according to the status of load, the operating state, etc.
An electric generator 20 is connected to the gas turbine 10, and is rotationally driven by the gas turbine 10 to generate electricity.
A heat exchanger 30 for heating intake air is interposed in the air intake duct 15. The heat exchanger 30 is supplied with steam S at a high temperature (e.g., 300° C.) via a steam pipe 31. The heat exchanger 30 heats (exchanges heat with) air A, which is taken into the gas turbine 10, by the heat of the supplied steam S.
In the steam pipe 31, a control valve 32 is interposed for controlling the amount of steam flowed through the steam pipe 31, namely, the amount of steam to be supplied to the heat exchanger 30.
As the steam supplied to the heat exchanger 30, there is used steam produced from an auxiliary steam boiler (not shown), or steam produced from a waste heat boiler (not shown) which generates steam by utilizing the waste heat of the turbine 13.
In the air intake duct 15, a thermometer 40 is mounted at a position between the heat exchanger 30 and the inlet stage of the compressor 11. The thermometer 40 measures the temperature of air A′ which has been heated by the heat exchanger 30 and is taken into the compressor 11 of the gas turbine 10. The measured temperature t1 of the intake air A′ measured in this manner is fed to a control device 50.
The control device 50 has a deviation computing section 51, and a proportional plus integral computing section (PI computing section) 52. This control device 50 has a target temperature TO (e.g., +5° C.) set beforehand therein. This target temperature TO is a temperature set beforehand according to the characteristics of each gas turbine 10, as the temperature of intake air which enables the gas turbine 10 to combust (operate) stably.
The deviation computing section 51 of the control device 50 computes the deviation between the measured temperature t1 and the target temperature TO to obtain a deviation temperature Δt (=TO−t1). The proportional plus integral computing section 52 performs PI computation of the deviation temperature Δt, and outputs a valve opening degree command P. The valve opening degree of the control valve 32 is adjusted according to the valve opening degree command P.
Thus, when the measured temperature t1 is low, the valve opening degree command P is great, making the valve opening degree of the control valve 32 high to increase the amount of steam which is supplied to the heat exchanger 30. When the measured temperature t1 is high, on the other hand, the valve opening degree command P is small, making the valve opening degree of the control valve 32 low to decrease the amount of steam which is supplied to the heat exchanger 30. After all, the amount of steam which is supplied to the heat exchanger 30 is feedback-controlled so that the temperature of air A′ heated by the heat exchanger 30 and taken into the compressor 11 becomes the target temperature TO. By so doing, the temperature of intake air A′ is maintained at a temperature which permits stable combustion.    Patent Document 1: JP-B-4-48921    Patent Document 2: JP-A-2003-161164